The direct metallization of electrically non-conductive substrates plays an important role in modern manufacturing processes of printed circuits boards. Usually, printed circuits boards are made of glass fiber reinforced epoxy resins, polyimides, or other suitable polymeric plastics. Such printed boards are often manufactured as multilayer circuits, in which different conduction pattern layers are superimposed. Individual conduction layers are connected to each other by plated through holes. Both for the application of the conduction patterns by means of masks or other suitable methods and for the generation of a sufficient conductivity within the plated through holes, chemical copper deposition methods and direct metallization methods are conventionally used.
Besides these applications, the direct metallization of plastics is also used in the field of decorative coatings, such as for example in the field of fittings manufacture, manufacture of jewelry, or in the automotive industry.
In the state of the art, it is conventional to directly coat non-conductive plastic substrates by electrolytic plating. Such a method is, for example, described in U.S. Pat. No. 3,099,608 and DE 33 04 004. However, the methods described therein have not been used in practice, since only freshly prepared solutions could obtain relatively usable results. Shortly after initiation, the quality of the metal deposition decreased, such that only insufficient results were achieved.
German published specifications DE 1 299 740, DE 2 926 335 A1, and DE 31 32 218 A1 disclose methods for the manufacture of plated through holes of printed circuits using conductive lacquers with subsequent electrolytic or electroless metallization.
German patent DE 38 06 884 C1 disclosed a method for the manufacture of throughplated printed boards on the basis of a polymeric or ceramic substrate by electrolytic or electroless application of a metal layer onto the surfaces. The substrate is pre-treated in an oxidizing bath, removed from the bath, and rinsed to remove bath residues. The substrate is then introduced into a bath which contains a monomer, in particular pyrrole or pyrrole derivates, that is electrically conducting in polymeric form. The thus treated substrate is introduced into an acid bath, wherein an electrically conducting layer of polymerized pyrrole or pyrrole derivatives is formed, followed by rinsing to remove bath residues, and electrolytic metallization.